Nitrogen -- the silent species ...( Nitrogen pollution from agriculture ...)

Nitrogen pollution from agriculture and fossil fuels is known to be seriously damaging grasslands in the UK. A new European study is starting to show that the effect is Europe-wide, confirming that current policies to protect ecosystems may need a re-think.

When Carly Stevens finished her PhD in 2004, her findings were so significant they were published in Science. Not only that, they were selected as contributing to one of the top ten scientific breakthroughs of that year quite something for a PhD student. Stevens had found the first evidence that nitrogen deposition from the atmosphere was depleting numbers of plant species in British grasslands. There was experimental evidence that this could happen, but we were the first to show the effect is real and happening now, says David Gowing, one of Stevens PhD supervisors at The Open University in the UK.

Stevens studied acid grasslands upland pastures with relatively infertile soils. She found that in places where more nitrogen is deposited, there are fewer plant species. The gradient was so pronounced that one species has been lost for each additional 2.5 kg of nitrogen per hectare deposited every year. Nitrogen from man-made sources, like intensive farming and cars, causes significant air pollution in the UK, and some is deposited from the air on to the land. Deposition is highest in densely-populated areas, and in Britain ranges from about 5 to 35 kg of nitrogen per hectare per year.

The approach to protecting wildlife from nitrogen pollution is to calculate critical load values for different ecosystems how much nitrogen a system can accumulate every year before damage occurs. Infertile habitats, like heathlands and bogs, are the most vulnerable. But Stevens research showed that species are being lost even where deposition is beneath the critical load for grasslands.

The species arent going extinct, Stevens stresses, but if this is happening everywhere, we are moving tow
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